There is strong ecological evidence suggesting that high vegetable-low fat diets are associated with lower breast cancer incidence and longer survival. The epidemiological evidence, however, is somewhat equivocal, possibly because of a limitation in the range of dietary patterns within given cultures. Although epidemiological studies have collinearity problems in trying to sort out a single nutrient as the effective anticarcinogen, the available data from both epidemiological and laboratory studies suggest that any anticarcinogenic effect of diet probably will not be explained by the ingestion of a single micronutrient (e.g. betacarotene) nor is it likely to be the result of the limitation or ingestion of a single macronutrient (e.g. fat). Rather, the data suggest that an anticarcinogenic effect may come from the ingestion of a dietary pattern that is high in vegetables and low in fat, where the daily consumption of fiber is greater than the consumption of fat. We argue that there is an urgent need for a randomized controlled trial to try to replicate the results of the ecological studies. The dietary goal of such a study should be to achieve a two fold difference between the study groups in the fiber-fat ration with the intervention group consuming more fiber grams than fat grams. Further, the intervention group diet should be such that the group sustains a 50% increase in blood carotenoid levels.